The Disappearance of Kelp Forests

Like many other ocean resources around the world, kelp forests are disappearing at a staggering rate. Since the 1960s, nearly 90% of California's kelp forests have been lost or damaged [5].

The Ideal Kelp Environment

There are certain aspects of an ecosystem that help to facilitate the growth of kelp in coastal waters. First, There has to be an acceptable surface to which the kelp can attach. The holdfast of the kelp act as a root like system and most commonly attaches to a rigid rocky surface. Secondly, cold and nutrient-rich water below 70 degrees Fahrenheit (21 degrees Celsius) is also required for kelp survival. It is speculated that waters above this temperature are too low in nutrients for kelp to thrive. Third, kelp is a marine inhabitant and is not found in fresh water or in waters of high salinity (>40 salinity units). When left to grow in normal sea water (about 35 salinity units), kelp grows as normal. Fourth, there is a need for clear water. Kelp is an algae, which like terrestrial plants, need sunlight to photosynthesize and produce nutrients and energy. Lastly, kelp need wave motion to circulate the cold water and nutrients throughout their environment. These all help explain the coastal proximity of kelp forests [5].

Kelp Forest Dangers

There is a plethora of factors, both human and natural (but usually facilitated by human activity) that could degrade kelp forest habitats and ultimately destroy these environments. Global warming and the associated rising of ocean temperatures can negatively affect these ecosystems. If temperatures continue to rise, the oceans may become too warm to allow kelp growth; therefore, existing kelp would die and restoration would be next to impossible because young kelp is especially vulnerable. A similar reality is true for the effects of ocean acidification. As ocean pH drops, the aquatic environment could become to acidic for kelp to survive. Human use of rivers and estuarine habitats can also affect kelp forests. As we continue to use rivers for such things as logging, dredging, and development, we dislodge large amounts of sediment into the rivers that is ultimately flushed into the oceans. This clouds the water and make photosynthesis nearly impossible for the kelp. These, along with over harvesting by humans, can drastically alter kelp forest; however, the most notorious destructive culprit is the sea urchin [5].

Sea urchins (pictured above) are herbivorous invertebrates that eat kelp holdfasts and can destroy entire forests in a rapid amount of time and are one of the leading causes of kelp forest loss. Photo courtesy of Carl Gwinn.

The Rise of the Urchin

Historically, humans have had a taste for meat and fur. This did not bode well for sea otter populations along the west coast of North America. Nearly hunted to extinction, the sea otter is a rare sight in the wild despite attempts to restore their populations. Many people would believe that the depletion of one species could not possibly affect an ecosystem as diverse as a kelp forest, but they are wrong. This is the classic example of a trophic cascade (a situation in which a keystone predator [sea otters] is removed and their prey [sea urchins] species booms). With the removal of sea otters, came the rise in sea urchin populations. The herbivorous sea urchins multiply unhindered and mercilessly feed on the holdfast that keep the kelp rooted to the ocean floor. Areas can yield upwards of 200 individual urchins per square yard and can effectively wipe out an entire forest in a matter of days [5].